Exhaust gases generated by an internal combustion engine may be subjected to aftertreatment measures in order to reduce pollutant emissions below predefined limits and adherence to increasingly stringent environmental protection requirements. For example, in applied-ignition engines, use is made of catalytic reactors which, through the use of catalytic materials increase the rate of certain reactions to ensure an oxidation of hydrocarbons (HC) and carbon monoxide (CO). For the oxidation of the unburned hydrocarbons and of carbon monoxide, provision is made in particular of an oxidation catalytic converter in the exhaust-gas flow.
In the case of internal combustion engines operated with an excess of air, for example direct-injection diesel engines or direct-injection applied-ignition engines, the nitrogen oxides (NOx) in the exhaust gas cannot be reduced without the addition of a reducing agent. The reduction of NOx emissions to form nitrogen (N2) and water (H2O) can take place, for example, with an ammonia-containing reducing agent as a reaction fluid on a selectively acting catalytic converter, or selective catalytic reduction (SCR) catalytic converter. Herein, the term “selective” means that the reducing agent introduced reacts preferentially with NOx despite the presence of molecular oxygen and, in some instances, other chemical species (e.g. HC).
The inventor has recognized that adequate exhaust gas conversion may be difficult to attain at low exhaust gas temperatures such as prevail in city traffic. The inventor has solved these problems by developing an exhaust gas aftertreatment system comprising a dosing unit with an adjustable piston whose adjustment further controls the distribution and amount of reaction fluid delivered therefrom. In one particular example, a cone angle of injected reductant directed into an engine exhaust upstream of a catalytic device may be adjusted based on the temperature distribution within the catalytic device. In another example, a method comprising adjusting a feed device located upstream of a catalytic converter responsive to a temperature distribution of a catalytic converter arranged in an exhaust duct to adjust a supply of fluid therefrom, and controlling a distribution and amount of the supplied fluid by adjusting a position and shape of a piston within the feed device is described for adjusting a flow of reductant according to the exhaust gas system of the present disclosure. In this way, the technical result is achieved wherein the fluid flow shape may be controlled to achieve a more optimal exhaust gas conversion based on the conditions prevailing within the exhaust gas system.
The above advantages and other advantages, and features of the present description will be readily apparent from the following Detailed Description when taken alone or in connection with the accompanying drawings. It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.